1. Field of the Invention
The invention relates to a rotary cutter for the pelletization of plastic extrudates, said rotary cutter being provided with knives projecting axially away from its end surface, said knives being individually affixed to supporting surfaces of the rotary cutter by means of fastening elements.
2. Description of Prior Art
Such a rotary cutter is described and presented in U.S. Pat. No. 3,196,487. Said rotary cutter is used in an underwater pelletizer having a die plate with circularly disposed extrusion orifices, said extrusion orifices being skimmed over in circular motion by the knives of the rotary cutter, said knives widely projecting in the manner of blades. The rotary cutter rotates about a shaft extending through the centre of the circle along which are disposed the extrusion orifices in the die plate. As they move over the extrusion orifices, the knives cut the extruded plastic strands issuing in molten form from the extrusion orifices into individual pieces which form the desired pellets or granules. This cutting operation takes place under water, said water flowing over the die plate during rotation of the rotary cutter. Owing to their considerable length, the knives, which project in the manner of blades, tend to flutter somewhat, this having an adverse effect on the close contact between knives and die plate. However, constant close contact between the knives and the die plate is a prerequisite for the uniform cutting of the plastic strands.
In another known underwater pelletizer according to DE-PS 10062113, the knives supported by the rotary cutter are individually screwed onto supporting surfaces affixed to the rotary cutter and provide a more compact, flutter-free design. The supporting surfaces extend towards the die plate in the rotary cutter, for which purpose the rotary cutter is provided with supporting surfaces extending in identical direction. The individual knives are pressed onto said supporting surfaces by means of screws which serve as fastening elements, said screws penetrating the knives, with the heads of the screws protruding from the knives such as to be easily accessible for a tool. Provided between the individual knives and the individual supports, forming the supporting surfaces, on the rotary cutter are intermediate spaces through which the water and pellets are able to flow away in the axial direction. It has emerged that the screw heads, which protrude from the individual knives, are, firstly, not easily accessible on account of the oppositely positioned supports and, secondly, obstruct the passage of water and pellets as the latter flow past them.